The present application is related to camless actuation of a valve. More particularly, the present application relates to actuation of a combustion engine intake/exhaust valve.
Electrohydraulic valve actuators are known. Such actuators have facilitated research into the possible development of camless engines where timing the lift and closure of intake and exhaust valves for different engine speed and load conditions has the potential to improve efficiency and torque and to reduce emissions.
In the past, such actuators have been directly coupled to the valve to be actuated. The stroke of the actuator equaled the stroke of the valve to be actuated. Such an actuator is depicted in prior art FIG. 1. The actuator of FIG. 1 includes what has been described as a digital valve. The digital valve is fluidly coupled to a source of actuation fluid under pressure. The drive piston is directly coupled to the stem of the engine valve. Admitting such actuating fluid to bear on the drive piston strokes the piston downward, compressing the return spring and opening the engine valve. When the digital valve vents the actuating fluid, the return spring closes the engine valve. The stroke of the drive piston and the stroke of the engine valve are equal. There is no amplification of the stroke motion of the actuator piston. It can be a burden for the actuator to generate the desired engine valve stroke, as is described below.
A further embodiment of an actuator includes a motion amplifying servomechanism as depicted in FIG. 2, described in more detail in the parent application of the present application. In this mechanization, stroke motion amplification is achieved by hydraulic means. In this implementation, (U.S. Pat. No. 6,044,815), the secondary piston is mechanically attached to a poppet valve that controls the influx and efflux of air and combustion gases into and out of a cylinder of an internal combustion engine. The secondary piston is likewise constrained to move linearly between lower and upper limits, the difference of which approximates the required displacement of the poppet valve.
Through use of the servomechanism described, the motion of the hydraulically actuated secondary piston is made to faithfully track, or follow, the motion of the electromagnetically actuated main piston. This servomechanism is described in greater detail in U.S. Pat. No. 6,044,815.
To date, the mechanism used to provide this motion multiplication has been a xe2x80x9chydraulic springxe2x80x9d located between a second stage piston and a follower piston that precisely tracks the motion of the poppet valve. See FIG. 2. This type of mechanism takes advantage of the principle of mass continuity for incompressible fluids. That is, a displacement of the drive piston 26 is amplified and transmitted to the poppet-valve according to:
A1X1=A2X2 
By proper choice of A1 and A2, suitable amplification is provided.
For practical purposes, it is extremely desirable to limit the stroke of both the first stage and the second stage pistons. Shorter stroke of the actuator valve 24 requires less magnetic force that means either a smaller solenoid may be employed and/or less electrical current is required. Shorter stroke of the hydraulically actuated second stage consumes less hydraulic fluid, though at higher actuating pressures. Both of these issues relate to cost and packaging of the needle valve actuator, and ultimately, to feasibility of implementation.
However, the poppet-valve motions required by the engine are dictated by engine performance and emissions restrictions, not cost and packaging. Therefore it is desirable to provide some mechanism to amplify the drive piston 26 motion and transmit this xe2x80x9camplifiedxe2x80x9d motion to the poppet valve.
More generally, it is extremely desirable to limit the stroke of any hydraulic actuation applied to a poppet valve of an internal combustion engine. The hydraulic power required to drive such a system is proportional to the stroke of the hydraulic actuator used. As the strokes required of such a hydraulic actuator are large (typically equal to the required stroke of the poppet valve), the hydraulic power required to operate such a system tends to be quite large as well. This hydraulic power, coupled with the electrical power required to drive any control system required by the hydraulics, constitutes a parasitic loss on the engine, thus reducing effective engine output. This issue directly relates to cost and packaging of any hydraulic valve actuator, and ultimately, to feasibility of implementation. The lack of any commercially available electrohydraulic camless system on the market today is a testimony to this fact.
Therefore it is desirable to provide some mechanism to amplify the hydraulic actuator motion and transmit this xe2x80x9camplifiedxe2x80x9d motion to the poppet valve.
The present invention substantially meets the aforementioned needs of the industry by providing for stroke amplification by mechanical means. Such means preferably include an actuator acting directly on a rocker arm, the rocker arm acting on the engine valve and amplifying the stroke of the actuator. The present invention amplifies the stroke of an actuator by mechanical means. The actuator may be a servomechanism and may be electronically controlled and hydraulically actuated.
The present invention is a valve actuator assembly for actuating a valve, the valve having a longitudinal axis includes an electrohydraulic actuator being displaced a lateral distance from the valve longitudinal axis, and a rocker arm being rotatable about a hinge point, a first arm portion extending from the hinge point to a proximal end and a second arm portion extending from the hinge point to a distal end, the proximal end being operably coupled to the second stage piston and the distal end being operably coupled to the valve, the fist arm portion being shorter than the second arm portion, the rocker arm spanning the lateral distance. The present invention is further a method of stroke amplification.